Previous attempts have been made to render customer viewable the amount of ink in an ink cartridge of an inkjet printer. Other attempts have been made to manufacture and implement a dependable electrical ink supply detection mechanism that informs customers, for example, via their computer screen or an electrical signal sent to their printer, when their cartridges are almost out of ink.
Attempts have been made using light beams reflected or refracted by prisms to produce both a customer viewable and electrically detectable means of ink supply detection. Furthermore, a prism structure has been positioned in an ink cartridge for purposes of ink level detection.
A principle of optics, called Total Internal Reflection (TIR), is relevant to this discussion of light beams and prisms. TIR occurs when an internal light ray strikes an internal segment of the prism at an angle greater than a certain critical angle with respect to an angle normal to the light beam and the internal segment. If the light beam hits the prism segment at or greater than the certain critical angle, and if the refractive index is lower on the outside than on the inside of the prism, such as when the prism is surrounded by air, no light at the critical angle or above can pass through to the outside of the prism. In that case, all of the light is reflected within the prism. Given the materials from which prisms are usually made (e.g., glass or polymeric materials), the critical angle for such prisms are usually between the angles of 40 and 50 degrees.
Previous attempts to utilize light and prisms with an ink cartridge to produce readable light signals related to ink level in the ink cartridge tend to produce signals which are unclear, from either an electrical detection or a human viewable perspective. The on/off signal produced is generally not strong.